1. Technical Field
The present invention relates to a light irradiation system of an image scanning apparatus employed for copiers, facsimile machines, image scanners, an image scanning apparatus having the light irradiation system, and an image forming apparatus having the image scanning apparatus.
2. Background Art
Image scanning apparatuses employed for copiers, facsimile machines, and image scanners include a light source that emits a light to a scan target such as a document face placed on a contact glass. The image scanning apparatuses further includes an image scanning unit having a image focus lens for focusing an image of scanning light reflected from the document face and progressing along a scan light axis, and an image capturing element such as a charge coupled device (CCD) that focuses the image of the image of scanning light to scan a document image.
The image scanning apparatuses typically employ a rod-shaped light source such as a fluorescent light and a xenon lamp or a point light source such as a light emitting diode (LED) as the light source. In view of demands to high speed activation, longer life time, energy saving to the light source, the LED has been replacing the fluorescent light and xenon lamp as the light source.
FIG. 1 is a schematic side view of a light irradiation system of conventional image scanning apparatuses. As shown in FIG. 1, the light irradiation system includes a first moving unit 103, a bracket 121, a circuit board 123, and a light emitting diode (LED) 122. The bracket 121 having a cross-sectional shape of V is attached to the first moving unit 103, the circuit board 123 is attached to the bracket 121, and the LED 122 is attached to the circuit board 123.
Further, the first moving unit 103 is attached with a reflector 118, which is a reflection plate that reflects light coming from the LED 122, to correct irradiation profile and to eliminate shadow which may occur when scanning a so-called cut-and-paste document.
In conventional image scanning apparatuses employing the light irradiation system shown in FIG. 1, a distance (i.e., light path) from a document face 102 to an image capturing element is relatively long. Therefore, in conventional image scanning apparatuses, attenuation of scanning light between the document face 102 and the image capturing element becomes greater, and therefore, light intensity of the LED 122 is required to be set greater.
As for the LED 122, one single LED has a small light flux amount and a narrower irradiation area. Therefore, in conventional image scanning apparatuses, a plurality of LEDs 122 are arranged in an array pattern in a main scanning direction of document to increase light intensity on the document face 102.
When the plurality of LEDs 122 are arranged in the array pattern, the LEDs 122 are arranged by slanting the LEDs 122 with respect to the document face 102 using the bracket 121 to obtain a preferable irradiation profile in a sub-scanning direction of the document face 102. The irradiation profile in the sub-scanning direction on the document face 102 is preferably set only at an actual scan area on document such as an irradiation area E on the document face 102 shown in FIG. 1.
However, even if the LED 122 is disposed at the slanted position, and an irradiation light from the LED 122 is reflected at the reflector 118 and then directed to the document face 102, some light is irradiated to an area other than the irradiation area E, which can be confirmed by observing the irradiation profile in the sub-scanning direction on the document face 102.
In this case, for example, when a small black solid image surrounded by a white area is scanned, light reflected from the white area existing in the irradiation area E enters an image capturing element. Therefore, an output value corresponding to the black solid image may be increased, with which the black solid image cannot be reproduced correctly.